In a conventional hydraulic press there is a steel piston chamber that contains oil and as oil is pumped into the piston chamber, the piston is pushed out of the piston chamber into pressurized contact with a work piece. In an alternate, or hydro-forming press, high-pressure water is forced into a closed chamber against a metal sheet or tube and, as the pressure builds in the chamber, the sheet is pressed and stretched into a cavity behind it. Another press positions a work piece between a conventional movable forming die and an expandable bladder optionally filled with fluid under pressure. Still another press uses an enclosed inflatable container in communication with hydraulic fluid reservoirs to provide the pressure for the ram in the hydraulic press so the hydraulic fluid is never in direct contact with any of the structural mechanisms of the press.
In conventional press designs, the chamber is closed with a rubber gasket or a low pressure seal, or as is the case with a hot isostatic press (HIP) a simple screw type plug lock. In a conventional HIP press, the pressure transfer medium is a hot gas such as nitrogen or argon, or water, or oil or a rubber crumb, and heating and cooling is achieved by thermal transfer to the work piece through the gas or other transfer medium, or a by a heated mold.
In forming advanced composite articles under high pressures and temperatures, it is recognized that certain silicone compounds are useful as uniform pressure transmitting media, and U.S. Pat. No. 4,770,835 to Kromrey is incorporated herein by reference as if fully set forth in order to provide further background about such compounds.
Conventional high strength, low weight structural composites are made from materials such as fiberglass or graphite. The composite article is typically made of multiple layers of so-called pre-pregs (combination resin and fiber materials) which have been laid up over a mold or die and thereafter cured under selected temperature and pressure conditions. Curing of the pre-preg layup is conventionally accomplished in an autoclave and requires the use of a vacuum bag or other type of barrier to prevent the pressurized fluid or gas from penetrating the layers and ruining the composite article which is being fabricated. But autoclaves are expensive and limited in pressure range and vacuum bags have a tendency to leak, resulting in a comparatively high reject rate.
One proposed solution has been to utilize so-called trapped rubber molding systems to cure such components. This is generally a closed container or mold within which is placed a cured elastomer such as a silicone rubber that has a high coefficient of thermal expansion. Heating the part in the mold in the container causes the surrounding elastomer to expand and, when the apparatus is properly configured, the elastomer then applies a uniform isostatic pressure to the pre-preg layup in the mold or on the die.
Another proposed solution is to encapsulate or pre-cast a work piece inside a crushable ceramic, and then apply pressure to the ceramic to simultaneously crush it and expose the work piece to consolidation pressure.
What does not yet appear is any means or method of providing a primary pressure source to a pressure transfer medium in a press that does not involve some kind of conventional ram (hydraulic, mechanical or otherwise) or thermal expansion aspect. What is needed is a press filled with a substantially incompressible medium such as silicone, where the medium at least partially encloses an elastomeric vessel filled with fluid such as oil or water and in fluid communication with a source of pressurized fluid, such that, as the vessel is pressurized inside the transfer medium, the pressure expands throughout the medium to provide a substantially uniform pressure to the work piece against the mold. What is also needed is a rapid cycling, high pressure press, that can be rapidly and readily opened to remove and replace a consolidated composite article with a new pre-preg layup, and then rapidly and effectively closed and sealed again for the next part cycle. What is needed is a high pressure low cost system capable of high production volumes and rapid part cycle times.